As is known, the curing agents commonly used in tyre rubber compounds comprise stearic acid and zinc oxide, which act as curing activators in a way that is still being researched.
Tests have shown, however, that stearic acid reacts with zinc oxide to form zinc stearate, which tends to migrate to the surface of the green compound to produce a surface phenomenon known as ‘blooming’.
One of the main drawbacks of blooming is that it reduces the surface adhesion properties of the compound.
At the tyre building stage, organic-solvent-based adhesive compounds (known as cement) are currently used to effectively connect green compounds.
Recent regulations, however, have reduced the use of organic-solvent-based cements, thus forcing tyre manufacturers to seek out alternative effective compound-connecting solutions.
In this regard, it should be noted that adhesive resins have potentially negative effects in terms of hysteresis.
One possible solution is to enhance the surface adhesion of the compounds for connection, so as to avoid, or at least reduce, use of solvent-based cements and/or adhesive resins.
Achieving this depends on minimizing blooming, i.e. zinc stearate migration to the surface of the green compound.
A compound is therefore needed which, despite comprising stearic acid and zinc oxide as curing activators, prevents blooming and the adhesion issues resulting from it.